Erdogan launched the attack after US announcement!

Turkey's President Recep Tayyip Erdogan announced the decision to launch a military operation just after the news of the formation of border security forces in the north-eastern border with Kurdistan-based militias. In a televised speech, he said that the Turkish military operation against Kurdish militias in Syria was "extremely sensitive".
Meanwhile, only after the US announcement to form BSF in coordination with Kurd-militia, Russian President Vladimir Putin and Bashar al-Assad, the Syrian dictator, have reacted sharply. However, Turkey's President Erdogan has expressed the most intense reactions. He called the BSF as a 'terrorist force' and threatened to destroy it.
In response, he said that the Syrian border forces in Turkey have started an attack already in the Kurdish main areas in north-western Syria. Besides this, the first shelling of Kurdish militias in the name of YPG has started. Why is his long-time friend Turkey so mad against this plan? Because of this, 15-20% of Turkey's population is Kurdish. In Turkey almost every year the Kurds try to get up. But the Turkish government is slowing down on their military campaigns and arrests.
Analysts think that if there is a strong arm of Kurds near the border of Turkey, it can be interrupted in Turkey's internal peace-chain. If there is a Kurdish army beside the border, Turkey's authorities would be feared that they could bolster civil war in Turkey with the military assistance of the Kurds in the country, fearing Turkish authorities. Meanwhile, despite his long-time ally informing the United States of America, Washington is not taking the issue.
According to Washington, the YPG (Kurds) have provided very important support in the fight against Islamic State. In the words of the Washington, this new militia will be called the SDF and the Syrian border with Turkey and Iraq, and the Euphrates river valley is safe. This is practically the Syrian government forces and the division of SDF controlled areas. The United States says a powerful bordering force can stop the movement of Islamic State here.
Meanwhile, Russian Foreign Minister Lavrov said that if this army can call it the Syrian division. Therefore, we are strongly opposed to the formation of the force.
It is worth mentioning that Kurds are one of the ethnic groups in Syria, Iraq, Iran, Armenia and Turkey - living in vast areas of these five countries. Most of them are known as Sunni Muslims. But they have their distinct lifestyle, language and culture. They never got their independent state. At least 40 thousand people have been killed since the launch of YiGira armed struggle in 1978. So the demand for independence is far behind the Kurds. But turkey thinks the Kurds can arise after getting the opportunity.